Air Vehicle Flight Mechanism and Control Method for Non-Sinusoidal Wing Flapping

ABSTRACT

A flapping wing driving apparatus includes at least one crank gear capstan rotatably coupled to a crank gear, the at least one crank gear capstan disposed radially offset from a center of rotation of the crank gear; a first wing capstan coupled to a first wing, the first wing capstan having a first variable-radius drive pulley portion; and a first drive linking member configured to drive the first wing capstan, the first drive linking member windably coupled between the first variable-radius drive pulley portion and one of the at least one crank gear capstan; wherein the first wing capstan is configured to non-constantly, angularly rotate responsive to a constant angular rotation of the crank gear.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional applicationSer. No. 15/581,976, filed Apr. 28, 2017, which is a continuation ofU.S. Nonprovisional application Ser. No. 13/969,258, filed Aug. 16,2013, which issued as U.S. Pat. No. 9,669,925 on Jun. 6, 2017, which isa continuation of International Application No. PCT/US2012/025518, filedFeb. 16, 2012, which claims priority to and the benefit of U.S.Provisional Application No. 61/443,669, filed Feb. 16, 2011, all ofwhich are hereby incorporated by reference herein in their entirety forall purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under contract no.W31P4Q-06-C-0435 awarded by the US Army Aviation and Missile Command.The US Government has certain rights in the invention.

TECHNICAL FIELD OF ENDEAVOR

The field of the invention is heavier-than-air aircraft, and moreparticularly unmanned aerial vehicles (UAVs) that have flapping wings.

BACKGROUND

Radio-controlled, heavier-than-air aircraft having sustainable beatingwings, i.e., ornithopters.

SUMMARY

Embodiments of the invention include a flapping wing driving apparatusthat comprises at least one crank gear capstan rotatably coupled to acrank gear, the at least one crank gear capstan disposed radially offsetfrom a center of rotation of the crank gear, a first wing capstancoupled to a first wing, the first wing capstan having a firstvariable-radius drive pulley portion, and a first drive linking memberconfigured to drive the first capstan, the first drive linking memberwindably coupled between the first variable-radius drive pulley portionand one of the at least one crank gear capstan so that the first wingcapstan is configured to non-constantly, angularly rotate responsive toa constant angular rotation of the crank gear. The invention may alsocomprise a second wing capstan coupled to a second wing, the second wingcapstan having a second variable-radius drive pulley portion, a seconddrive linking member windably coupled between the second variable-radiusdrive pulley portion and one of the at least one crank gear capstan, afirst synchronization pulley and a second synchronization pulleydisposed on the first wing capstan and the second wing capstans,respectively, and a first crossing synchronization linking member and asecond crossing synchronization linking member each windably coupledbetween the first synchronization pulley and the second synchronizationpulley, the first crossing synchronization linking member and the secondcrossing synchronization linking member, so that the first wing capstanis configured to non-constantly, angularly rotate responsive to aconstant angular rotation of the crank gear. In such an embodiment, thefirst drive linking member may be received by the first variable-radiusdrive pulley portion at a maximum radius of the first variable-radiusdrive pulley portion as the first wing capstan changes rotationaldirection. The first synchronization drive pulley and secondsynchronization drive pulley may be configured with a constant radiusand, in such an embodiment, the first synchronization drive pulley andthe second synchronization drive pulley may each be configured towindably receive the first synchronization linking member and the secondsynchronization linking member at non-constant radius drive pulleyportions. A first drive linking member winding peg may be configured torotatably take up the first drive linking member so that slack in thefirst drive linking member between the first variable-radius drivepulley portion and one of the at least one crank gear capstan isreduced. Embodiments may include means for reducing slack in the firstdrive linking member between the first variable-radius drive pulleyportion and one of the at least one crank gear capstan. The first drivelinking member and the second drive linking member may each comprise aplurality of cables and the plurality of cables may be elastic.

Embodiments of the invention include a flapping wing driving apparatusthat may comprise a motor and a plurality of reduction gears coupledbetween the motor and the crank gear so that at least one of theplurality of reduction gears is configured to drive the at least onecrank gear capstan in an orbital path about a center of rotation of thecrank shaft. The first and second drive linking members may each be aplurality of cables.

Embodiments of the invention include a flapping wing driving apparatusthat may comprise a first wing and a second wing, a first wing capstanand a second wing capstan respectively coupled to the first wing and thesecond wing, each of the first wing capstan and the second wing capstanhaving respective variable radius drive pulley portions, at least onerotatable crank gear capstan coupled to a crank arm at a location offsetfrom the axis of rotation of the crank arm, a first drive linking cableand second drive linking cable wherein each drive linking cable isrespectively coupled to one of the at least one crank gear capstan, thefirst drive linking cable windably coupled to the variable-radius drivepulley portion of the first wing drive capstan and the second drivelinking cable windably coupled to the variable-radius drive pulleyportion of the second wing drive capstan, a first synchronization pulleyand a second synchronization pulley each respectively coupled to thefirst wing capstan and the second wing capstan, and a first crossingsynchronization linking member and a second crossing synchronizationlinking member each windably coupled between the first synchronizationpulley and the second synchronization pulley, the first crossingsynchronization linking member and the second crossing synchronizationlinking member wherein the second wing capstan is configured to rotatein a direction counter to a rotation of the first wing capstan, whereinconstant angular rotation of the crank arm alternately pulls the firstand second drive linking cables to drive the first and second wingcapstans with a return force for each of the first and second wingcapstans provided respectively by the second and first crossingsynchronization linking members so that the first and second wings movein a non-sinusoidal back-and-forth flapping motion. In one embodiment,coupling of the first drive linking cable and second drive linking cableto the first variable-radius drive pulley portion and the secondvariable-radius drive pulley portion, respectively, is configured sothat the first and second drive linking cables are received atrespective maximum radii of the first and second variable-radius drivepulley portions as the first and second wings, respectively, areconfigured to change direction of travel so that the speed and theacceleration of the first and second wings about the end of the wingtravel is reduced. The respective variable-radius drive pulley portionsof the first wing capstan and the second wing capstan may also each belob-shaped, oval-shaped, or each of the first second synchronizationpulley and second synchronization pulley may be variable-radiussynchronization pulleys. In one embodiment, the first variable-radiussynchronization pulley and the second variable-radius synchronizationpulley are lob-shaped. The invention may also include a motor configuredto rotatably drive the crank arm, and the at least one rotatable crankgear capstan may comprise two co-axial, rotatable, crank gear capstans.Each of the first drive linking cable and the second drive linking cablemay be elastic.

In a further embodiment, a flapping wing method comprises orbiting acrank capstan about an axis of rotation, pulling a first drive cablewith the crank capstan, the first drive cable windably coupled to avariable-radius drive pulley portion fixed on a rotatable first wingcapstan to cause the rotatable first wing capstan to rotate, therotatable first wing capstan coupled to a first wing, winding up a firstsynchronization cable about a synchronization pulley on the first wingcapstan in response to the rotating of the rotatable first wing capstan,and synchronizably rotating a rotatable second wing capstan windablycoupled to the first synchronization cable in response to the winding upthe first synchronization cable about the synchronization pulley, therotatable second wing capstan coupled to a second wing, so that thefirst wing is configured to rotate with a non-sinusoidal angularvelocity about a rotation axis of the rotatable first wing capstan asthe crank capstan orbits about the axis of rotation at a constantangular velocity and the second wing rotates with about a rotation axisof the rotatable second wing capstan. The method may also comprisepulling a second drive cable with the crank capstan after pulling thefirst drive cable, the second drive cable windably coupled to avariable-radius drive pulley portion fixed on a rotatable second wingcapstan to cause the rotatable second wing capstan to rotate, therotatable second wing capstan coupled to a second wing, winding up asecond synchronization cable about a synchronization pulley on thesecond wing capstan in response to the rotating of the rotatable secondwing capstan, and synchronizably rotating the rotatable first wingcapstan windably coupled to the second synchronization cable in responseto the winding up the second synchronization cable about thesynchronization pulley on the second wing capstan so that the secondwing is configured to rotate with a non-sinusoidal angular velocityabout a rotation axis of the rotatable second wing capstan as the crankcapstan orbits about the axis of rotation at a constant angular velocityand the first wing rotates about a rotation axis of the rotatable firstwing capstan. The pulling of the second drive cable may begin when thefirst drive cable is received at a maximum radius of the variable-radiusdrive pulley portion on the first wing capstan. Pulling the second drivecable may begin as the first wing changes rotational direction. Thesynchronization pulley on the second wing capstan may be non-circular.The second drive cable may also be elastic. Pulling of the first drivecable may begin when the second drive cable is received at a maximumradius of the variable-radius drive pulley portion on the second wingcapstan. The synchronization pulley on the first wing capstan may benon-circular.

Embodiments of the invention may also include a flapping wing drivingapparatus that comprises means for orbiting at least one crank gearcapstan about a center of rotation and at a constant velocity, a firstwing capstan coupled to a first wing, the first wing capstan having afirst variable-radius drive pulley portion, and a first drive linkingmember configured to drive the first wing capstan, the first drivelinking member windably coupled between the first variable-radius drivepulley portion and one of the at least one crank gear capstan so thatthe first wing capstan is configured to non-constantly, angularly rotateresponsive to a constant velocity of the means for orbiting. Theinvention may also comprise a second wing capstan coupled to a secondwing, the second wing capstan having a second variable-radius drivepulley portion, a second drive linking member windably coupled betweenthe second variable-radius drive pulley portion and one of the at leastone crank gear capstan, a first synchronization pulley and a secondsynchronization pulley coupled to the first wing capstan and the secondwing capstans, respectively, and a first crossing synchronizationlinking member and a second crossing synchronization linking member eachwindably coupled between the first synchronization pulley and the secondsynchronization pulley, the first crossing synchronization linkingmember and the second crossing synchronization linking member, so thatthe first wing capstan is configured to non-constantly, angularly rotateresponsive to a constant angular rotation of the crank gear.

Another embodiment of the invention includes a flapping wing drivingapparatus that comprises a first wing and a second wing, a first wingcapstan and a second wing capstan respectively coupled to the first wingand the second wing, means for rotating the first wing capstan and thesecond wing capstan in a predetermined non-sinusoidal acceleration froma first sweep angle position to a second sweep angle position of thefirst wing and the second wing, means for returning the first wingcapstan and the second wing capstan to their respective first sweepangle positions after the respective first sweep angle position tosecond sweep angle position predetermined non-sinusoidal acceleration,so that the means for rotating and the means for returning areconfigured so that the first wing and second wing move in anon-sinusoidal back-and-forth flapping motion. The means for returningmay further comprise means for returning the first wing capstan and thesecond wing capstan to their respective original angular positions in apredetermined non-sinusoidal acceleration from the second sweep angleposition to the first sweep angle position.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example and not limitation in thefigures of the accompanying drawing, and in which:

FIG. 1 is a perspective view of one embodiment of an air vehicle thathas two flappable wings that flap in a horizontal plane about the airvehicle;

FIG. 2 is a perspective view of an air vehicle that has a flappingmechanism mid-body, vehicle components located above the flappingmechanism, and batteries on a tail post;

FIGS. 3A, 3B, and 3C are front plan, front perspective and side views,respectively, illustrating components placement, flapping mechanismplacement, and battery placement on a lower body gimbal frame system ofan air vehicle;

FIGS. 4A, 4B, and 4C are front plan, front perspective and side views,respectively, illustrating vehicle components placement, flappingmechanism placement, and battery placement on a lower body gimbal framesystem of an air vehicle;

FIGS. 5A and 5B are perspective views of an air vehicle frame having oneembodiment of an integrated boom yang system;

FIGS. 6A and 6B are perspective views of an air vehicle frame having alower body gimbal system;

FIGS. 7A, 7B, and 7C are perspective views of three embodiments of acrank arm to drive a flapping mechanism;

FIG. 8 is a front perspective view of one embodiment of a crank arm andpulley assembly of a flapping mechanism;

FIG. 9 is a perspective view of one embodiment of a wing capstan havingpulley portions and string winding pegs to windably couple a pluralityof cables to the wing capstan;

FIG. 10 is a rear perspective view of the embodiment of the crank armand pulley assembly first illustrated in FIG. 8;

FIG. 11 is an exploded view of the device show in FIGS. 8 and 10;

FIGS. 12A-12F show an embodiment of the flapping mechanism having wingcapstans each driven by a crank gear in a first rotational direction bydrive linking cables and in an opposite rotational direction by crossingsynchronization linking members;

FIGS. 13A, 13B and 13C are exemplary graphs of flap angle (degrees) andtip accelerations (g) verses flap cycle to illustrate the effects of thevariable-radius drive pulley portions on wing position and acceleration;

FIGS. 14A and 14B illustrate one embodiment of a coupling configurationfor coupling wing masts to respective wing root spars and boom vangs toenable yaw control of a flapping mechanism;

FIGS. 15A and 15B illustrate one embodiment of a pitch-tiltable cameracoupled to the top of an air vehicle frame that has a lower body gimbalsystem configuration;

FIGS. 16A, 16B, and 16C illustrate one embodiment of a yaw controlarrangement and structure thereof for an air vehicle that includes a yawservo driving push-pull cables through respective cable guides;

FIGS. 17A, 17B, and 17C illustrate an embodiment for providing yawcontrol of an air vehicle frame using lever arms coupled to respectivepushrods to drive respective drive wing root spars;

FIGS. 18A and 18B are front and rear perspective views, respectively,illustrating one embodiment of an integrated boom yang system driven bya yaw servo through pushrods to provide yaw control of a flappingmechanism;

FIGS. 19A and 19B are front and rear perspective views of an air vehicleframe having a yaw control system driving a lower body gimbal system andsupporting a plurality of batteries;

FIGS. 20A and 20B are front and rear perspective views of anotherembodiment of an air vehicle frame having a yaw control system drivingan integrated boom yang system;

FIGS. 21A-21D are perspective views of one embodiment of a plurality oftail elements that may fold toward a center axis of an air vehicle aftertaking off from a surface;

FIGS. 22A, 22B, and 22C are rear perspective views of a lower bodygimbal system having a root spar coupled to an attitude control armthrough a universal joint to provide yaw control of an air vehicle; and

FIG. 23 illustrates one embodiment of an air vehicle that has wingsconfigured to fold against a body of the air vehicle.

DETAILED DESCRIPTION

Embodiments of the present invention include radio-controlled,heavier-than-air aircraft having flapping wings, i.e., ornithopters,where the vehicle orientation control may be affected by variable sweepangles of deflection of the flappable wings in the course of sweepangles of travel. The air vehicle may comprise at least two wings, orairfoils, having the principal functions of providing lift andgenerating control moments or torques about the air vehicle. Either oftwo such airfoils may be disposed on each side of the fuselage, orstructural body, of the air vehicle. Each wing may comprise aroot-to-wingtip spar, or mast, having a proximal end proximate to thewing root, and a distal end proximate to the wingtip. Each wing maycomprise a root spar, or boom, proximate to the proximal end of themast, and the boom may be oriented, fixedly rotationally, but otherwisesubstantially orthogonal to the mast. A lifting surface membrane elementfor each wing may be attached to the respective mast and the boom, andthe membrane and boom may rotate or pivot about the longitudinal axis ofthe mast. The wings may be driven by an onboard flapping drive element,e.g., at least one motor and mechanical movement so as to be flapped sothat their wingtips circumscribe arcs about the longitudinal axis of theair vehicle. If the boom is free to travel some angular amount about themast, for example, then the distal end of the boom and the trailing edgeof the lifting surface tend to trail the motion of the mast and leadingportion of the lifting surface during flapping strokes. The distal endof the boom may be variably restrained relative to the mast, therebyvariably limiting the angular travel of the boom about the mast and/orvarying the wing membrane slack, or luffing of the membrane. A thrustforce may be generated via the airfoils, each airfoil's thrust having aninstantaneous magnitude depending on the direction of mast flapping,i.e., a forward stroke or a backward stroke, the angle of each boomrelative to its respective mast and/or the amount of luffing in the wingmembrane and/or the angular velocity of the wing during the stroke.

FIG. 1 depicts an exemplary air vehicle comprising two flappable wings,a flapping drive subsystem, and a pitch, yaw, and roll controlsubsystem. The exemplary air vehicle may be powered via batteries andmay receive radio control signals via a radio control system. FIG. 1depicts an aircraft 100 having two airfoils 101, 102 a left (port)airfoil 101 and a right (starboard) airfoil 102, each attached to anaircraft structure 103, such as a fuselage, and where the flapping inthe forward direction of the aircraft, where the wingtips of theairfoils generally circumscribe arcs 104, 105 in the horizontal planeabout the aircraft 100, and their respective extents of travel eachdefine a sweep angle of travel.

FIG. 2 depicts an embodiment of an air vehicle 200 having a flappingmechanism 202 mid-body, a computer processing unit, a radio receiver, aradio transmitter, and a camera, all positioned above the flappingmechanism 202. Battery packs (204, 206) may be positioned on or about atail post 208. Such battery packs may each be, for example, 50milliamp-hour (mAHh) cells. A body shell (not shown) may be installedon, about and/or over the vehicle frame. The air vehicle 200 isconfigured to maintain a center of gravity about the vehicle,horizontal, and fore/aft axes. A third battery pack 210 may be disposedabove the flapping mechanism.

FIGS. 3A, 3B, and 3C are front plan, front perspective, and side views,respectively, of an air vehicle illustrating vehicle componentplacement, flapping mechanism placement, and battery placement on alower body gimbal frame system (See FIGS. 5C, 5D). The vehiclecomponents, such as the computer processing unit, radio receiver, radiotransmitter, and camera, may be located in a component volume 300located above the flapping mechanism volume 305. In FIGS. 3B and 3C, ayaw servo 307 may be positioned at or near the top of the vehicle(represented as a dashed cylinder) projecting to the back of thevehicle. In one embodiment, a camera may be positioned at the upperfront of the vehicle, and a battery pack may be on the starboard side(each not shown). The flapping mechanism in the flapping mechanismvolume 305 may be arranged in the middle portion of the air vehicle, andthe additional batteries (310, 315) positioned at the front and back ofthe tail element, respectively, with the additional batteries (310, 315)and tail element 320 defining a tail portion 325.

FIGS. 4A, 4B, and 4C are front plan, front perspective and side views,respectively, of an air vehicle illustrating vehicle componentplacement, flapping mechanism placement, and battery placement on alower body gimbal frame system (See FIGS. 5C, 5D). Similar to theembodiment illustrated in FIGS. 3A-3C, the vehicle components, such asthe computer processing unit, radio receiver, radio transmitter, andcamera, may be located in a component volume 400 located above theflapping mechanism volume 405. In FIGS. 4B and 4C, an additional battery407 may be positioned at or near the top of the vehicle in addition to ayaw servo (not shown). The flapping mechanism in the flapping mechanismvolume 405 that drives the flappable wings (408, 409) may be arranged inthe middle portion of the air vehicle, and the additional batteries(410, 415) may be positioned at the front and back of a distal end ofthe tail element 420, respectively, with the additional batteries andtail element 420 defining a tail portion 425. In FIGS. 4A, 4B and 4C,the spine 430 may range from a top portion of the vehicle to the tailelement 420 in an integrated boom bang system embodiment (See FIGS. 5A,5B).

FIGS. 5A and 5B are perspective views of an air vehicle frame having oneembodiment of an integrated boom yang system. The air vehicle frame 500may have a lower arcuate spine 505 extending from a proximal end 510 ofa tail portion 515 outwardly to a position above and adjacent to agimbal joint 520, with the gimbal joint 520 connecting an upper spine525 to a rotatable boom yang support 535. A control gimbal 530 mayreceive rotatable boom yang support 535 for trimming the position of theboom vangs 537 in relation to the air vehicle frame. FIG. 5B depicts aconfiguration with a pitch deflection for the rotatable boom yangsupport 535 about the gimbal joint 520 for pitch control of the airvehicle during flight.

FIGS. 6A and 6B are perspective views of an air vehicle frame 600 havinga lower body gimbal system. A rotatable boom yang support 605 that maybe rotatably coupled to an upper spine 610 through a gimbal joint 615.The boom yang support 605 may be received by a control gimbal 620 fortrimming. In FIG. 6A, boom yang support 605 is aligned with the upperspine 610. In FIG. 6B, the boom yang support 605 is illustrated asrotated out of alignment with the upper spine 610 to indicate a pitchdeflection for pitch control of the air vehicle during flight.

FIGS. 7A, 7B and 7C are perspective views of embodiments of a crank armfor driving a flapping mechanism of an air vehicle. In FIG. 7A, a crankarm 700 is illustrated having three arms 705 positioned 120 degrees fromone another to receive crank position magnets (not shown) to enablecollection of angular rotation information for the crank arm. One of thearms 705 may have a support element 710 disposed radially offset from acenter of rotation of the arms to receive at least one capstan to acceptdrive linking cables (See FIG. 8). FIG. 7B depicts the inclusion of anouter gear 715 to the embodiment of the crank arm shown in FIG. 7A tofacilitate driving the crank arm by reduction gears from a motor (SeeFIG. 10). FIG. 7C depicts the outer gear having the addition of crankposition magnets 720 at alternate locations for increasing the crankposition accuracy when the outer gear 715 is included with the crank arm700.

FIG. 8 is a perspective view of one embodiment of a gear and pulleyassembly of a flapping mechanism. A drive motor 800 may drive a crankarm that may be a crank gear 805. A first crank gear capstan 810 may bepositioned co-linear with a second crank gear capstan 815 and rotatablycoupled to the crank gear 805, where both the first and second crankgear capstans (810, 815) are offset from a rotational axis of the crankgear 805. In an alternative embodiment, the first and second crank gearcapstans (810, 815) are a single capstan. A first wing capstan 820 maybe disposed at a first axis of rotation of the first flapping elementand a second wing capstan 825 may be disposed at a first axis ofrotation of the second flapping element. A first drive linking member830 may be a cable that attaches to the first crank gear capstan 810 ata first end of the cable and windably couples to a first variable-radiusdrive pulley portion 822 of the first wing capstan 820 at a second endof the cable to drive the first wing capstan 820 (See e.g., FIG. 12A). Asecond drive linking member 835 may also be a cable that attaches to thesecond crank gear capstan 815 at a first end of the cable and windablycouples to a second variable-radius drive pulley portion 837 of thesecond wing capstan 825 at a second end of the cable to drive the secondwing capstan 825 (See e.g., FIG. 12A).

A crossing synchronization linking member that may be a firstsynchronization cable 840 may be windably coupled between first andsecond wing capstans (820, 825) at the first and second synchronizationpulleys (842, 843), respectively, with the first synchronization cable840 spooled in a clockwise orientation on each of the first and secondsynchronization pulleys (842, 843). A second synchronization linkingmember that may be a second synchronization cable 845 may be windablycoupled between first and second wing capstans (820, 825) at the firstand second synchronization pulleys (842, 843), respectively, with thesecond synchronization cable 845 spooled in a counterclockwiseorientation on each of the first and second synchronization pulleys(842, 843), such that first and second synchronization cables (840, 845)are crossed over the crank gear 805. In some embodiments, the firstsynchronization cable 840 attaches the first wing capstan 820 in acounterclockwise orientation to the second wing capstan 825, and thesecond synchronization cable 845 attaches the second wing capstan 825 ina clockwise orientation to the first wing capstan 820. In either ofthese embodiments, the first synchronization cable 840 attaches thefirst wing capstan 820 in an orientation opposite to that of the secondsynchronization cable 845 attaching to the second wing capstan 825, suchthat first and second synchronization cables (840, 845) function assynchronization strings for the first and second flapping elements. Inthis manner, the first and second wing capstans (820, 825) areconfigured to non-constantly, angularly rotate responsive to a constantangular rotation of the crank gear 805.

In an alternative embodiment, the first synchronization cable 840 mayattach to the first wing capstan 820 in a clockwise, orcounterclockwise, orientation to the second wing capstan 825 viamultiple strings, e.g., via four strings, and the second synchronizationcable 845 may attach to the second wing capstan 825 in acounterclockwise, or clockwise, orientation to the first wing capstan820 via multiple strings, e.g., via four stings. Also, the first drivelinking cable 830 may attach to the first crank gear capstan 810 via twostrings and the second drive linking cable 835 cable may attach to thesecond wing capstan 825 via two strings. The first and second wingcapstan (820, 825) may each allow for the fixing of the strings to therespective capstans.

The top of the drive motor (as shown in FIG. 10) comprises a gear thatdrives a set of reduction gears such as a secondary gear that drives athird gear that may include distributed magnets, for example at thedistributed portions of the third gear. The first and second crank gearcapstans (810, 815) are rotationally disposed from the lower plane ofthe third gear that may be the crank gear 805.

FIG. 9 is a perspective view of a wing capstan having pulleys,synchronizing strings and drive strings windably coupled to the firstwing capstan. The first drive cable 830, illustrated as consisting oftwo individual strings, may be windably coupled onto a first drivepulley portion 900 that may have a variable-radius, i.e. not round. Inthe embodiment illustrated, with the first drive cable 830 having twoindividual strings, two individual pulley portions may collectively bereferred to as the first drive pulley portion 900 and each may have avariable-radius shape where windably receiving the strings of the firstdrive cable 830. Termination portions of the first drive cable 830 maybe fixedly coupled to a string winding peg 905 to enable winding of thefirst drive cable 830 about the first drive pulley portion 900 as thewing capstan 820 rotates. The string winding peg 905 may enable trimmingof the first wing capstan 820 as the winding peg 905 is rotated to spoolmore or less of the first drive cable 830 for any given angular locationof the first wing capstan. The first and second crossing synchronizationlinking members (840, 845) are each windably coupled to a firstsynchronization pulley 910, with the first crossing synchronizationlinking member 840 illustrated as windably coupled to the first wingcapstan in a counterclockwise orientation and the second crossingsynchronization linking member 845 illustrated as windably coupled tothe first wing capstan in a clockwise orientation. Termination portionsof the first and second synchronization linking members (840, 845) maybe fixedly coupled to a second string winding peg 915 to enable windingand unwinding of the first and second synchronization linking members(840, 845) about the first synchronization pulley 910 as the wingcapstan 820 rotates. Synchronizing strings function to move the capstanof the flapping assembly in alternating clockwise and anticlockwisedirections, which in turn move the wings attached to the wing capstans(820, 825) in synchronized opposing directions, that is, in a flappingmanner.

FIG. 10 is a rear perspective view of the embodiment of the crank armand pulley assembly first illustrated in FIG. 8. A motor gear 1000coupled to the motor 800 may drive the crank gear 805 through a motorreduction gear 1005. As the motor gear 1000 rotates with a constantangular rotation to drive the crank gear 805, the first and second wingcapstans (820, 825) are alternately pulled by the first drive linkingmember 830 (See FIG. 8) and the second drive linking member 835,respectively, at a predetermined non-sinusoidal acceleration from afirst sweep angle position to a second sweep angle position (e.g., froma front original position to back sweeping position) and a return forceis provided by the first and second crossing synchronization linkingmembers (840, 845) to return the first and second wing capstans (820,825) to the first sweep angle position to establish a back and forthflapping motion for wings (not shown) that may be connected to the firstand second wing capstans (820, 825).

FIG. 11 is an exploded view of the device show in FIGS. 8 and 10. Thisfigure shows four sets of strings: first and second crossingsynchronization strings (840, 845) and first and second drive linkingmembers (830, 835) that may be strings. The first crossingsynchronization string 840 may be windably coupled for moving (e.g.,pulling) the first wing capstan 820 in a first direction (e.g.,clockwise) and the second crossing synchronization string 845 may bewindably coupled for moving (e.g., pulling) the first wing capstan 820in a second (opposite) direction (e.g., counterclockwise). Where thefirst and second set of synchronization strings (840, 845) cross overeach other between the first and second wing capstans (820, 825) suchthat the first crossing synchronization string 840 operates to move(e.g., pull) the second wing capstan 825 in a first direction (e.g.,clockwise) and the second crossing synchronization string 845 operatedto move (e.g., pull) the second wing capstan 825 in a second (opposite)direction (e.g., counterclockwise). One of the two sets of drive strings830 is for moving (e.g., pulling) the first wing capstan 820 in a firstdirection (e.g., counterclockwise) as a result of the movement of thefirst or second capstan (810, 815) on the crank gear 805 and the otherset of drive strings 835 is for moving (e.g., pulling) the second wingcapstan 825 in the first direction (e.g., counterclockwise) as a resultof the movement of the other capstan (815, 810), where the action (e.g.,pulling) of the first and second drive strings (830, 835) occur oppositeof one other (such that when one drive string is pulling a wing capstanto cause its rotation, the other drive string is feeding onto and beingreceived by its respective wing capstan). Mechanism connections mayinclude integral motor mount saddles and an integral control mechanismbase.

FIGS. 12A-12F depict the two wing drive capstans that engage thesynchronizing strings and the drive strings. The crossingsynchronization strings may attach to the pulleys near the controlmechanism, and the drive strings may attach near the upper portion ofthe pulley.

FIG. 12A shows a top view (looking from either the top or from thebottom of the air vehicle, depending on the embodiment) of the flappingmechanism. The flapping mechanism 1200 may include a crank gear 1202that rotates about a center pivot or axis 1204 and may have one or two(co-axial) capstans 1206 rotatably mounted to the crank gear on a pivotor the axis 1207 at a position off set from the center 1204 of the crankgear 1202. Attached to the crank gear capstans 1206 are two drivelinking members that may be drive strings (1208, 1210), each drivestring (1208, 1210) running to one of the two wing drive capstans (1212,1214) (alternatively referred to as “wing capstans”) that in turn eachmove respective wing masts (1216, 1218) extending therefrom, in a backand forth flapping motion as the crank gear 1202 rotates. The drivestrings (1208, 1210) operate in a manner where one string is pulling oneof the wing drive capstans, then the other drive string is pulling theother wing drive capstan as the crank gear 1202 rotates, with a returnforce on each of the wing drive capstans (1212, 1214) being applied byone of the crossing synchronization strings (1220, 1222). In thismanner, constant angular rotation of the crank gear results innon-constant angular rotation of the first and second wing capstans whenthe first and second wing capstan are driven by the crank gear.

Each drive string (1208, 1210) is windably received on its respectivewing drive capstan (1212, 1214) by a respective drive string pulleyportion (1224, 1226) that may have a variable radius that defines alobe, egg, oval or other non-constant radius shape. The shape of thedrive string pulley portions (1224, 1226) functions to both reduce orlimit the accelerations of the wing masts (1216, 1218) (and hence theattached wings) at or about the end of each of their flap cycles (e.g.,where the wing changes its direction of travel), as well as to maintaina desired and/or sufficient tension on the drive string. In variousembodiments the drive strings may elongate to avoid slack. Inembodiments with round, or substantially round, drive string pulleys,the drive strings may become slack, adversely affecting the operation ofthe wing as it flaps and/or imparting vibrations into the flappingmechanism and the air vehicle. However, with lobe or similar shapedpulleys the drive strings are taken up and/or received by the pulley toprevent or limit any slack in the string. Although the drive strings(1208, 1210) are described in terms of strings, they may also bedescribed as cables, bands or simply as “members.” Also, althoughillustrated as having a single strand, each string may consist of aplurality of strands to form the cable, band or member.

Also windably attached to the first and second wing drive capstans(1212, 1214) are the two crossing synchronization strings (1220, 1222)at first and second synchronization pulleys, respectively (1228, 1230).The first and second synchronization pulleys (1228, 1230) may be round(e.g., configured with a constant radius) or may have a non-constantradius where receiving the first and second synchronization strings(1220, 1222).

FIG. 12B is a side view of the flapping mechanism illustrating the twodrive linking members and crossing synchronization strings. The firstand second drive strings (1208, 1210) may be windably coupled atrespective wing drive capstans (1212, 1214). The first wing drivecapstan 1212 may have the drive pulley portion 1224 to windably receivethe first drive string 1208 and a first sychronization pulley 1228 towindably receive the first crossing synchronization linking member thatmay be a crossing synchronization linking string 1220. Similarly, thesecond wing drive capstan 1214 may have the second drive pulley portion1226 to windably receive the second drive string 1210 and a secondsychronization pulley 1230 to windably receive the second crossingsynchronization linking string 1222.

FIG. 12C-12E illustrate different flapping mechanism component positionsduring operation. As the crank gear 1202 rotates counterclockwise at aconstant angular velocity, the second drive string 1210 may be pulledand windably configured on the second wing drive capstan 1224 to rotateit counterclockwise and to both move the second wing mast 1216 in acounterclockwise rotation and to windably pull the first synchronizationstring 1220. The at least one crank gear capstan 1206 is freelyrotatable on the crank gear 1202 and so the second drive string 1210does not spool around the crank gear 1202 during operation. The firstsynchronization string 1220 may be windably configured on the secondwing drive capstan 1212 to rotate it clockwise resulting in clockwiserotation of the first wing mast 1216. The crank gear 1202 transitionsfrom pulling the second drive string 1210 to pulling the first drivestring 1208 as the second drive string 1210 is received at a maximumradius Rmax (See FIG. 12F) of the second variable-radius drive pulleyportion 1226. The second wing capstan 1214 changes rotation direction(e.g., to a clockwise rotation) in response to the crank gear capstansnow pulling the first drive string 1208. Similarly, the first crossingsynchronization string 1220 begins to spool onto the first wing capstan1212 in response to counterclockwise rotation of the first wing drivecapstan 1212 resulting in a change of the rotation direction (e.g., to aclockwise rotation) of the second wing capstan 1214.

In embodiments, the pulley portions for the synchronization strings maybe round in shape (constant radius), such that the tension of thesynchronization strings, and the force exerted and speed imparted ontothe wing drive capstan by the synchronization strings remain constant(or at least substantially constant) throughout the travel (rotation) ofthe capstan. In such embodiments, each of the two pulleys for each setof synchronization strings are the same (or at least substantially thesame) in size and shape. In contrast, in embodiments, the pulleyportions for the drive strings may be shaped in a manner that providesthat the tension on the drive strings, as well as the force exerted andspeed imparted onto the wing drive capstan by the drive strings varythrough the travel (rotation) of the capstan. This variable tension,force and speed can be achieved in some embodiments by varying theradius of the drive pulley about the capstan (i.e. a “variable-radius”capstan), such that the drive pulley has an oval or egg shape. With avariable radius shape the speed and the acceleration of the wings, whichmay be attached to the drive capstan pulleys, may be varied with theposition and movement of the wing drive capstans. In at least oneembodiment, the drive pulleys may be shaped so that when the wings arenear or at the end of their travel in the flapping motion, that is,where they change direction of travel, that the radial distance from thecenter of rotation of the drive capstan pulley to the surface of thedrive pulley (e.g., where the drive string is received by the capstanpulley), is at its greatest, which results in reducing the speed and theaccelerations of the wing at and about the end of the wing travel. Suchreduced speed and accelerations of the wings function to conserveenergy, reduce noise, wear and vibrations. In addition, by shaping thedrive pulley to have a larger radial distance at the end of the wingdrive capstan and wing travel, additional tension may be applied by thedrive pulley to the drive strings, which in turn functions to prevent orat least reduce slack in the drive string, which in turn improves theperformance of the device by reducing accelerations of the drive capstanand wing and/or slapping or snapping of the drive string.

FIGS. 13A-C are example graphs of flap angle (degrees) and tipacceleration (g) verses flap cycle to illustrate the effects of thevariable-radius drive pulley portions disposed on the wing capstans, inthese example graphs lobe-shaped pulleys, on wing position andacceleration. For these examples, synchronization strings are alsopositioned between the two wing capstans with the synchronizationstrings crossing over therebetween such that they function to cause thewing capstans (and thus the wings) to move in opposite directions tocreate a flapping motion. The synchronization strings are received byround shaped pulley portions of the wing drive capstans. In otherembodiments, other shapes of these pulleys may be used. In theembodiment shown, the synchronization strings do not contact orotherwise engage the crank gear, instead they pass over the crank gearas shown. FIG. 12B shows a side view of an embodiment of the flappingmechanism.

In FIG. 13A, the left and right wing angles and tip accelerations areshown for an embodiment with circular shaped drive string pulleys on thewing drive capstan. As can be seen the right wing experiences slackstring on rear turn-around (negative flap angle) and vice versa for theleft. The slack string causes a large jerk on the wing where it maysuddenly tighten, and thereby result in a large acceleration spike.Because the acceleration spikes are experienced by one wing at a time,alternating yaw moments vibrate the air vehicle. FIG. 13B shows the leftand right wing angles and tip accelerations graphs for an embodimentwith lobe-shaped drive string pulleys on the wing drive capstan. Thepulley lobes provide tension to the string during the turn-around, andthe string is not allowed to go slack. The result is a more even flapprofile and more closely offsetting accelerations. FIG. 13C shows forthe left wing, a comparison between the embodiment with lobe-shapeddrive string pulleys and the embodiment with circular shaped drivestring pulleys. The graphs (FIGS. 13A-C) show the reduction in tipaccelerations with the use of the lobe-shaped drive string pulleys(FIGS. 12A-F), even when the stroke amplitude is larger.

FIGS. 14A and 14B illustrate one embodiment of a coupling configurationfor coupling wing masts to respective wing root spars and boom vangs toenable yaw control of a flapping mechanism. In FIG. 14A, a universaljoint 1400 may be positioned between the boom yang 1405/root spar 1410structure and the wing mast mount structure 1415, where the wing mastmount structure 1415 may be coupled to a variable-radius drive pulleyportion 1420 (FIG. 14B) on a wing drive capstan 1425. The universaljoint 1400 allows for two axis of rotation for the boom yang 1405 andthe root spar 1410, where the boom yang 1405 maintains alignment to theroot spar 1410. In FIG. 14B, a second universal joint 1430 may bepositioned between a second boom yang 1435/root spar 1440 structure anda second wing mast mount structure 1445. The second wing mast mountstructure 1445 may be coupled to a variable-radius drive pulley portion1450 (FIG. 14B) on a second wing drive capstan 1455. A wing mast 1460 iscoupled to the wing mast mount structure 1415 to rigidly support a wing(not shown).

FIG. 15 illustrates one embodiment of a pitch-tiltable camera coupled tothe top of an air vehicle frame 1500 that has a lower body gimbalconfiguration such as that illustrated in FIGS. 6A and 6B. A rotatableboom yang support 1505 may be rotatably coupled to an upper spine 1510through a gimbal joint 1515. A landing gear 1517 may be coupled to theboom yang support. A camera 1520 may be positioned at or near the top1525 of the structure of the air vehicle 1510. Using the gimbal joint1515 (alternately referred to as a “pitch gimbal”), the camera may betilted to different angles. That is, when the air vehicle frame 1500 ison the ground (perching) and the landing gear 1517 is fixed so that thelower body gimballing becomes static and the upper body moves about thepitch gimbal 1515, then the camera 1520 may be tilted as the upper spine1510 moves. In one embodiment, a roll gimbal (not shown) may be added tothe upper body and to enable the camera to be rolled. Also, a camera yawcontrol capability (not shown) may be added to the pitch and rollcapability to enable full pan, tilt, roll controls to the camera. Theyaw control may be a pivot with a cable to move the camera about thepivot, where the cable is actuated by the air vehicle's yaw controlservo.

FIGS. 16A-C illustrate an embodiment of a yaw control arrangement andstructure thereof for an air vehicle. FIG. 16A depicts the yaw controlcommand neutral position (e.g for hovering, vertical, forward/backward,or rolling flight without yaw). The yaw control structure components foreach wing (not shown) may include a lever arm 1600 mounted to a boomyang 1605 at a pivot point 1610 such that the lever arm 1600 rotatesabout the pivot point 1610. One end of the lever arm 1600 may beattached and/or in contact with a wing root spar 1615 such to deflect itrelative to the boom yang 1605 and about the universal joint (as setforth above) as the lever arm 1600 is pivoted. An opposing end of thelever arm 1600 may be attached to an actuator yaw servo 1620 through apush/pull cable 1625. FIG. 16B depicts a counterclockwise or left yawrotation (as viewing the air vehicle from above), as the lever arms 1600are deflected in opposite directions from one another. Different turningof the flap assemblies for each wing with respect to the drive assemblyresults in yawing of the air vehicle. FIG. 16C depicts a clockwise orright yaw rotation (as viewing the air vehicle from above), as the leverarms 1600 are deflected in opposite directions from one another, andopposite from that shown in FIG. 16B.

FIGS. 17A-C depict an embodiment for providing yaw control of a airvehicle frame using lever arms coupled to respective pushrods to driverespective drive wing root spars. For each wing, a lever arm (1700,1705) is mounted to a boom yang (1710, 1715) at a pivot point (1720,1725) such that the lever arm (1700, 1705) may rotate about the pivotpoint (1720, 1725). One end of each lever arm (1700, 1705) may beattached and/or in contact with a respective wing root spar (1730, 1735)such to deflect it relative to its respective boom yang (1710, 1715).Each boom yang (1710, 1715) is coupled to a respective pitch/rollcontrol arm 1750 that has a central pivot through respective ballsockets having a steel hinge bushing through their centers (1755, 1760)to allow the respective pitch/roll control arms to rotate in relation tothe boom vangs (1710, 1715). Each wing has a respective pushrod (1765,1770) to drive respective drive wing root spars (1730, 1735) throughrespective lever arms (1700, 1705).

In particular, FIG. 17A shows the root spars (1730, 1735) actuated in amanner to produce a right yaw of the air vehicle. FIG. 17B shows theroot spars generally aligned with their respective boom vangs (1710,1750) to produce no yaw or neutral yaw of the air vehicle. FIG. 17Cshows actuation of the root spars (1730, 1735) in a manner to produce aleft yaw of the air vehicle.

FIGS. 18A and 18B illustrate one embodiment of an integrated boom yangsystem driven by a yaw servo through pushrods to provide yaw control ofa flapping mechanism. Two wings (1800, 1805) are coupled to a flappingmechanism 1810, with a lower arcuate spine 1815 coupled to an attitudecontrol arm 1820 through a control gimbal 1825. A yaw servo 1830 drivesa lever arm 1835 through a pushrod 1840 and yaw arm assembly 1845.Referring to the starboard wing 1800, a fabric portion 1850 is supportedby a wing mast 1855 to establish a leading edge, and a root spar 1860supplements structural support for the fabric portion 1850. Thestarboard wing 1800 is rotatably connected to a boom yang 1865 throughthe lever arm 1835. The port wing 1805 is illustrated without a rootspar, boom yang, lever arm and push rod to better illustrate the fabricsleeve spar tube 1870 used to receive its respective root spar (notshown). As the pushrod 1840 drives the lever arm 1835, the attitudecontrol arm is caused to rotate to enable yaw control for the flappingmechanism 1810.

FIGS. 19A and 19B illustrate a yaw control system driving a lower bodygimbal system and supporting a plurality of batteries. A yaw servo 1900may be positioned at or near the top of the vehicle 1905 and projectingto the back of the vehicle (to the right of the image). Two wings (1910,1915) are coupled to a flapping mechanism 1920, with a boom yang support1925 coupled to an attitude control arm 1930 through a control gimbal1935. The yaw servo 1900 drives lever arms (1940, 1945) throughrespective pushrods (1950, 1955) and yaw arm assembly 1960 to provideyaw functionality of the vehicle. Two batteries (1965, 1970) are coupledto a lower end of the boom yang support 1925. A tail portion 1975supports the vehicle when landed.

FIGS. 20A and 20B illustrate another embodiment of a yaw control systemto drive an integrated boom yang system. In FIG. 20A, a yaw servo 2000may be positioned at or near the top of the vehicle 2005 and projectingto the back of the vehicle (to the right of the image). Two wings (2010,2015) are coupled to a flapping mechanism 2020, with a boom yang support2025 coupled to an attitude control arm 2030 through a control gimbal2035. The yaw servo 2000 drives lever arms (2040, 2045) throughrespective pushrods (2050, 2055) and yaw arm assembly 2060 to provideyaw functionality of the vehicle. Two batteries (2065, 2070) are coupledto a lower end of a lower arcuate spine 2075 extending from a proximalend of a tail portion 2080 outwardly to a position above and adjacent toa gimbal joint (not shown), with the gimbal joint connecting an upperspine 2085 to the rotatable boom yang support 2025.

In FIG. 20B, the wing material has been removed and a rear perspectiveview provides a better view of the starboard and port pushrods (2050,2055) coupled to the starboard and port lever arms (2040, 2045),respectively. Wing masts (2087, 2088) are exposed and may be coupled torespective boom vangs (2095, 2100) through respective universal joints(2105, 2110). As the starboard pushrod 2055 selectively pushes and pullsthe starboard lever arm 2040, the port pushrod 2050 would pull and pushthe port lever arm 2045 resulting in the attitude control arm 2030rotating in clockwise and counterclockwise directions, respectively,(viewed from below) to enable yaw control for the flapping mechanism2125. Four tail portions 2115 may be coupled to a tail post 2120 tosupport the vehicle when landed.

FIGS. 21A and 21B depicts an embodiment of an air vehicle having fourtail elements that may reorient toward a center of the vehicle axis asthe vehicle lifts from a surface. In FIG. 21A, a plurality of tailelements 2100, four elements in the illustrated embodiment, may each berotatably coupled to a flapping mechanism 2105 through a hinge assembly2110 and tail post 2115. As illustrated in FIG. 21B, as the air vehiclebecomes airborne and leaves its landing surface, the plurality of tailelements 2100 may each rotate toward a center of the vehicle axis.

FIG. 21C depicts a landed configuration for the hinge assembly and aproximal portion of the plurality of tail elements first illustrated inFIGS. 21A and 21B. Each tail element may have a hinge 2120 rotatableabout a pin 2125, with hinge 2120 having a hinge stop surface 2130abutting the tail post 2115 when in the air vehicle is landed. A skid2135 extends horizontally from the hinge 2120 so that a clockwiserotational moment applied by the flapping mechanism 2105, such as if theflapping mechanism is leaning toward the skid 2135, results incompression of the tail post 2115 on the hinge stop surface 2130,tension in the hinge 2120 at the pin 2125 and compression of the skid2135 against the landing surface to counteract the rotation momentapplied by the flapping mechanism 2105 to prevent the air vehicle fromfalling over.

FIG. 21D illustrates the hinge assembly and the proximal portion of theplurality of tail elements illustrated in FIG. 21C in an “in flight”configuration. As the vehicle lifts from the landing surface and theskid 2135 loses full contact with the landing surface, the hinge 2120and skid 2135 assembly is pulled by gravity to rotate about the pin 2125to reorient toward a center of the vehicle axis and the hinge stopsurface 2130 looses contact with the tail post 2115.

FIGS. 22A, 22B, and 22C illustrate one embodiment of a lower body gimbalsystem that may have a root spar 2200 coupled to an attitude control arm2205 through a universal joint 2210 to provide yaw control of an airvehicle. In FIG. 22A, the root spar 2200 is positioned parallel to aboom yang support 2215 and so may produce a neutral yaw position for theaircraft. In FIG. 22B, the root spar 2200 has been actuated toward theviewer and so may depict a right yaw. In FIG. 22C, the root spar 2200has been actuated away from the viewer and so may depicts a left yaw.

FIG. 23 depicts an embodiment of the wings having folding arrangementsfor storage, and/or returning to a flight configuration. As shown, eachwing mast 2300, 2305 may be connected to the flapping mechanism 2310 atits root with a hinge that allows each respective wing mast (2300, 2305)to rotate downward generally in the plane of the wing. The wings mayhave an additional hinge that may provide two substantially lockingpositions for the wings to “snap” open or closed by manual manipulation.In another embodiment, the wings may be motorized to close, or closeautomatically, when flapping stops.

One of ordinary skill in the art will appreciate that the elements,components, steps, and functions described herein may be furthersubdivided, combined, and/or varied, and yet, still remain within thespirit of the embodiments of the invention. Accordingly, it should beunderstood that various features and aspects of the disclosedembodiments may be combined with, or substituted for one another inorder to form varying modes of the invention, as disclosed by example.It is intended that the scope of the present invention herein disclosedby examples should not be limited by the particular disclosedembodiments described above. Accordingly, the invention has beendisclosed by way of example and not limitation, and reference should bemade to the following claims to determine the scope of the presentinvention.

What is claimed is:
 1. A system, comprising: a crank gear capstanrotatably coupled to a crank gear; a first wing capstan coupled to afirst wing, the first wing capstan having a first variable-radius drivepulley portion; and a first drive linking member configured to drive thefirst wing capstan, the first drive linking member coupled between thefirst variable-radius drive pulley portion and the crank gear capstan.2. The system of claim 1, wherein the first wing capstan is configuredto non-constantly, angularly rotate responsive to a constant angularrotation of the crank gear.
 3. The system of claim 1, wherein a radiusof the first variable-radius drive pulley portion increases about eachend of the first wing travel.
 4. The system of claim 1, wherein thefirst drive linking member is received by the first variable-radiusdrive pulley portion at a maximum radius of the first variable-radiusdrive pulley portion as the first wing capstan changes rotationaldirection.
 5. The system of claim 1, wherein an acceleration of thefirst wing about each end of first wing travel is reduced via the firstvariable-radius drive pulley portion.
 6. The system of claim 1, whereinthe crank gear capstan is disposed radially offset from a center ofrotation of the crank gear.
 7. The system of claim 1, furthercomprising: a second wing capstan coupled to a second wing, the secondwing capstan having a second variable-radius drive pulley portion; and asecond drive linking member coupled between the second variable-radiusdrive pulley portion and the crank gear capstan.
 8. The system of claim7, further comprising: a first synchronization pulley and a secondsynchronization pulley disposed on the first wing capstan and the secondwing capstans, respectively; and a first crossing synchronizationlinking member and a second crossing synchronization linking member eachwindably coupled between the first synchronization pulley and the secondsynchronization pulley.
 9. The system of claim 8, wherein the first wingcapstan and the second wing capstan are configured to non-constantly,angularly rotate responsive to a constant angular rotation of the crankgear.
 10. The system of claim 8, wherein the first synchronization drivepulley and second synchronization drive pulley are configured with aconstant radius.
 11. The system of claim 8, wherein the first drivelinking member and the second drive linking member each comprise aplurality of cables.
 12. The system of claim 8, wherein the first drivelinking member and the second drive linking member each are elastic.